Gum cameras often have different options for memory. Some only have internal memory. Other gum cams will have only external memory and will require you to purchase an external micro SD card (some vendors will provide that with the gum cam for free). Other gum cams can have an internal memory as well as ability to put in a micro SD card for external memory.
When you get a gum cam be sure to check for these things because if you have a gum cam that only has external memory and the vendor is not providing any external memory card, then you will not be able to use the gum cam to take pictures or any video.